Free-floating gas seal

ABSTRACT

A rotary aircraft exhaust system having an engine, an exhaust member in gaseous communication with the engine, and a longitudinally compressible bellow seal in sealing contact with both the engine and the exhaust member. The bellow seal is configured to provide a gaseous seal between the engine and the exhaust member while also allowing the exhaust member to move in the transverse, longitudinal, and pivoting directions relative to the engine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/662,829, filed 14 Mar. 2007, titled “Free-Floating Gas Seal,” whichclaims the benefit of International PCT Application No. PCT/US04/32606,filed 1 Oct. 2004, titled “Free-Floating Gas Seal,” both of which areboth hereby incorporated by reference for all purposes as if fully setforth herein.

BACKGROUND

1. Field of the Present Description

The present invention relates to seals. In particular, the presentinvention relates to seals useful in controlling the flow of exhaust gasexiting from a jet engine.

2. Description of Related Art

Many types of aircraft use turbines to provide the power necessary forflight. One example would be a rotary wing aircraft with a turbinedriving the rotating wing. In such aircraft the turbine engine issecurely fastened to the airframe of the rotary aircraft and an exhaustsystem may be attached to the exhaust end of the engine to redirectexhaust gases as desired. So long as the exhaust system is relativelylightweight, the engine can support the extra load. Because the exhaustsystem is attached directly to the engine the seal between the exhaustsystem and the engine is relatively simple. The main concern at thisjoint is the support of the exhaust system.

Recent advancements in exhaust systems have led to heavier exhaustsystems that reduce the heat signature of the aircraft as viewed throughinfrared equipment, among other advantages. Such exhaust systems makethe aircraft more difficult to spot and follow with infrared equipment,which is very important in military applications.

Due to the added weight of the infrared suppressing exhaust system, theexhaust system is no longer light enough to attach to the engine forsupport. Instead, the exhaust system must be mounted directly to theairframe. Because the engine and the exhaust are mounted to differentparts of the airframe, and because airframes flex during use, theexhaust and the engine are no longer relatively static. The exhaustsystem may move in three dimensions relative to the output end of theengine. Therefore, a rigid connection between the engine and the exhaustsystem would put stresses on the engine and the exhaust system.

Several problems arise when trying to mate the exhaust system to theengine and provide for both axial and radial movement in the joint. Theproblems stem from the relative motion that must be accommodated, thehigh temperatures of the environment, and the need for an adequate seal.A first problem is leakage from seals such as a finger seal, which donot adequately seal the exhaust gases. A second problem is the largediameter of the seal when trying to use a labyrinth joint or rope sealthat provides for sufficient radial movement. A third problem is theweight of the seal if a complex arrangement is used to accommodate themovement, but still provide adequate sealing. A fourth problem is themaintenance of the seal; longer service periods are needed and a passivefailure is desired.

Although there have been significant developments in the area of sealingexhaust systems to turbine engines, considerable shortcomings remain.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. However, the invention itself, as well as,a preferred mode of use, and further objectives and advantages thereof,will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings,wherein:

FIG. 1 is a turbine engine powered rotary wing aircraft with an infraredreducing exhaust system;

FIG. 2 is a cross-sectional view of the engine and exhaust system of theaircraft of FIG. 1;

FIG. 3 is a sectional close up of the exhaust seal shown in FIG. 2;

FIG. 4 is an axial view of the exhaust seal shown in FIG. 2; and

FIG. 5 is an axially exploded view of the components of the exhaust sealshown in FIG. 2.

DETAILED DESCRIPTION

The present invention represents the discovery that a free-floating sealcomprising a bellow and face seals can provide for low leakage ratesbetween components in a gas flow system while allowing significantlongitudinal and transverse movement of the components relative to eachother. The seal is particularly suited for use in a high temperatureenvironment, such as an exhaust seal between a turbine engine and aseparately supported exhaust system that experience axial and radialmovement relative to each other.

Referring to FIG. 1 in the drawings, a rotary wing aircraft 11 with aturbine engine 13 and exhaust system 15 is illustrated. Aircraft 11 hasan airframe 17. Engine 13 and exhaust system 15 are each attached toairframe 17 at separate points for structural support. Aircraft 11 isnot limited to rotary wing aircraft, as turbines are widely used onother types of aircraft, such as fixed-wing and tiltrotor aircraft.Additionally, the seal disclosed below may be used wherever exhaustsystem 15 and engine 13 may experience significant relative axial andradial movement.

Referring now FIGS. 2 and 3 in the drawings, a preferred embodiment ofthe invention is shown. Engine 13 is shown attached to exhaust system 15in a sectional view. Engine 13 has an outer heat shield 19 which isattached to aft firewall 21. Within heat shield 19 the engine terminateswith a deswirl duct 25. A circumferential member, such as split ring 23,is attached to deswirl duct 25. As shown in FIG. 3, split ring 23 has aninner circumference 27 and a preferably circumferential axial face 29.An optional flow-directing means may be located near split ring 23. Forexample, liner 31 is a cylindrical sleeve that extends axially along theinner circumference 27 toward exhaust system 15.

Continuing with FIG. 2 in the drawings, exhaust system 15 has an outerliner 33 and an inner liner 35. An adapter can 37 attaches to heatshield 19 and abuts outer liner 33. An aft seal ring 39 is attached toinner liner 35. Aft seal ring 39 has a preferably circumferential axialface 41.

Referring now to FIG. 3, a corrugated bellows 43 is positioned betweenaxial face 41 of aft seal ring 39 and axial face 29 of split ring 23.Bellows 43 is preferably a free-floating, circumferential unit, thoughone end of bellows 43 may be fixedly attached relative to engine 13 orto exhaust system 15. A lip 45 is formed on each axial ends of bellows43, with lips 45 being formed to be parallel to axial faces 29, 39.Bellows 43 is compressed slightly between axial faces 29, 41 to provideaxial pressure between each lip 45 and the corresponding axial face 29,41. Lips 45 and axial faces 29, 41 cooperate to form face seals forpreventing the escape of exhaust gases at the junction of engine 13 andexhaust system 15.

Continuing with FIG. 3, a close-up sectional view of bellows 43 showshow it relates to the nearby parts. Bellows 43 has corrugations 47between lips 45 that may be compressed axially and allow for some radialmovement of lips 45 relative to each other. Axial face 29 has a radialthickness that allows for radial movement of corresponding lip 45. Astop means, such as stop 49, is located on an inner portion of face 29to limit the radial movement of lip 45. Additionally, axial face 41 hasa radial thickness that allows for radial movement of corresponding lip45 and a corresponding stop 51 to limit radial movement of correspondinglip 45. Because all radial movement is relative between axial face 29and axial face 41, the radial thickness may be split evenly betweenaxial faces 29, 41 or one of the axial faces 29, 41 may have more radialthickness than the other. As shown, axial face 29 has a slightly moreradial thickness than axial face 41.

Also apparent from FIG. 3 is the function of liner 31 in directingexhaust gases past bellows 43. As the exhaust gases flow from engine 13to exhaust system 15, the flow travels along the inner face of liner 31,which extends for at least a portion of the length of bellows 43,preventing the flow from directly impinging on bellows 43. This reducesthe pressure on bellows 43 and thereby reduces the overall leakage ratearound bellows 43. Although shown in the drawings as a cylindrical liner31, various types of flow-directing means may be substituted for liner31 to limit the amount of flow pressure on bellows 43.

One important aspect of bellows 43, as shown, is that if lips 45 wearcompletely away, corrugations 47 will contact axial faces 29, 41 andprovide some degree of sealing. This is known as a passive failurebecause the sealing effectiveness is reduced gradually, instead of aninstantaneous complete failure of the seal.

Referring now to FIG. 4 in the drawings, an axial view of bellows 43 andsplit ring 23 shows the use of centering bumpers 53 attached to liner31. While stops 49, 51 limit the radial movement of lips 45, centeringbumpers 53 are positioned to limit the radial movement of corrugations47 between lips 45. Bumpers 53 urge bellows 43 toward the center of thelimits of travel and are particularly useful to prevent sagging ofbellows 43 when engine 13 is positioned horizontally.

Referring now to FIG. 5 in the drawings, a partially exploded view ofthe parts surrounding bellows 43 shows how the parts fit together. Asshown, split ring 23 may be formed of multiple parts bolted together toallow ease of assembly and disassembly for maintenance purposes.Additionally, liner 31 may be bolted to inner circumference 27 of splitring 23 for ease of replacement. Adapter can 37 is shown as clearlylarger in diameter than split ring 23, bellows 43 and aft seal ring 39,thus creating a space as shown in FIG. 3.

Because of the heat generated by engine 13 a heat resistant material ispreferred when constructing bellows 43. One example is Inconel®, whichmay be rolled from a sheet into a cylinder which may then be corrugated.Finally, lips 45 may be formed. Inconel® is well known for having hightemperature resistance and high strength. Other similar materials may beused in this application. Additionally, a coating, such as chromiumcarbide, on the adjacent surfaces lips 45 and axial faces 29, 41, mayimprove both the sealing characteristics and the wear characteristics ofthe system.

It is apparent that an invention with significant advantages has beendescribed and illustrated. Although the present invention is shown in alimited number of forms, it is not limited to just these forms, but isamenable to various changes and modifications without departing from thespirit thereof.

What is claimed is:
 1. A rotary aircraft exhaust system, comprising: anengine, the engine having a first seal face; an exhaust member ingaseous communication with the engine, the exhaust member having asecond seal face; a longitudinally compressible bellow seal in sealingcontact with both the engine and the exhaust member, the bellow sealbeing configured to slidingly engage the first seal face and the secondseal face; and a first stop protruding from the first seal face; asecond stop protruding from the second seal face; wherein the first sealface and the second seal face move in the transverse, longitudinal, andpivoting directions relative to each other; wherein the first stop andthe second stop limit radial sliding movement of the bellow seal; andwherein the bellow seal is configured to provide a gaseous seal betweenthe engine and the exhaust member while also allowing the exhaust memberto move in the transverse, longitudinal, and pivoting directionsrelative to the engine.
 2. The rotary aircraft exhaust system of claim1, the seal comprising: a first end formed as a face seal for sealingagainst the corresponding first seal face.
 3. The rotary aircraftexhaust system of claim 1, further comprising: a flow-directing meansfor protecting the seal from a nearby gas flow.